1. Field of the Invention
This invention relates to holders used with medical sensors for electrically monitoring sounds such as the heartbeat or respiratory noises within a patient's body. More particularly, the invention relates to a receptacle used to hold a piezoelectric acoustic sensor in contact with a patient's body to provide an improved signal to noise ratio as compared to the conventional method of applying the sensor directly to the patient's skin.
2. Description of Related Art
The stethoscope has long been an important tool used by physicians to hear sounds within a patient's body for diagnosing disease and monitoring the health of the patient. However, interpreting the sounds is a relatively subjective task so that the comments one physician places in the patient's file may not be the same as those of another. Moreover, even though it is possible to record the sounds and to keep those recordings in the patient's file, tapes and other conventional sound recording media are bulky and awkward to store.
As a result, a new technology has been introduced into the market in which sounds and vibrations transmitted through a patient's body, such as the sounds produced by the heart or lungs, are detected by a sensor and, after appropriate amplification and filtering, are displayed visually. One method of display is to show the frequency spectrum of the sound as a function of time. Regardless of the form of the display, however, this procedure permits a visual display of the sounds which can be photographed, printed or stored electronically in the patient's file for further study. In general, this allows the sounds to be processed and handled in much the same way as an electrocardiogram is presently handled.
Such systems often provide spectral analysis of the sound signal and/or may provide highlighted marking of certain frequencies of interest of the physician to identify unusual noises or noises most likely to correspond to diseases. The most modern systems provide real time three dimensional display of the spectrum of heart and/or lung sounds on a high resolution color graphics monitor with specified frequencies and/or patterns being highlighted in a readily discernible color.
Systems of this type require a good sensor capable of producing a high quality electrical signal corresponding to the sounds transmitted through the patient's body. The sensor used is typically a piezoelectric sheet material having a surface area of a few tens of square centimeters. Sounds and vibrations passing through the patient cause the piezoelectric sensor to flex, generating a voltage which can be amplified, filtered and processed as desired.
Particularly where the sounds are to be analyzed spectrally, it is important for the sensor to provide a high signal level at all frequencies and to reduce noise to the minimum. It has heretofore been believed that the best method for obtaining the desired high signal to noise ratio is to apply the sensor directly to the skin of the patient at one or more desired acoustic sensing locations. This minimizes the number of interfaces that the sound must cross. At each interface there is the possibility that the sound will be attenuated. Commonly the acoustic sensor has been adhered directly to the skin of the patient with a temporary medical adhesive of the type used to attach electrocardiogram and other medical sensors.
This method has been found to have several problems, however. The step of applying the adhesive to the sensor is messy and time consuming. Moreover, once the adhesive is applied to the sensor it can be removed only with great difficulty and consequent risk of damage to the sensor. As a result, the sensor is usually discarded after a single use. A typical examination may use up to four or more sensors with a resulting high cost for each examination.
More importantly, the magnitude of the signal from sensors attached directly to the skin is limited and obtaining sufficient output is occasionally difficult. Yet another difficulty is that there are several types of noise that may be picked up by the sensor and mask the desired signal from the patient. Room noise is a common problem, particularly in emergency room settings or in pediatric care situations where the ambient noise levels are high. Because of the sensitivity of the sensor, objectionable noise is also produced whenever anything moves relative to the sensor or the patient in the vicinity of the sensor. "Cable noise" is the result of motion between the electrical cable connected to the piezoelectric sensor and the sensor. "Hair noise" occurs when the patient's body hair brushes the sensor as the patient breathes or moves. Other sources of objectionable noise exist, and all of these noise sources degrade the signal to noise ratio. In some settings the degradation can be so severe as to make it impossible to perform the desired analysis.
Another difficulty is that if a sensor is determined to be defective or if a different type of sensor must be used or tested, each sensor must be positioned at the same desired monitoring location on the patient's skin. Detaching an adhesively applied sensor from the skin once is uncomfortable. Detaching an adhesively applied replacement sensor from the same location where the previous sensor was positioned may be prohibitively uncomfortable to the patient.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a receptacle for holding an acoustic sensor whereby the signal output by the sensor is increased.
A further object of the invention is to provide an acoustic sensor receptacle which decreases the detection of room noise, particularly in pediatric settings or in an emergency room and also decreases cable noise and noise associated with motion between the sensor and the patient's body such as noise produced by contact between the cable and the body or between hairs on the patient's body and the sensor.
It is another object of the present invention to provide an acoustic sensor receptacle which permits the sensor to be reused repeatedly without cleaning and without damage to the sensor.
A further object of the present invention is to provide an acoustic sensor receptacle which is relatively inexpensive and may be discarded after each use.
Still another object of the invention is to provide a medical acoustic sensor receptacle which produces an improved signal to noise ratio on heavier patients.
Yet another object of the present invention is to provide a medical acoustic sensor receptacle that permits a defective sensor to be easily and painlessly replaced without changing the sensing location of the sensor.